The present invention relates to solenoid valves and, more particularly, to a solenoid valve for delivering a fluid at a variable flow-rate, of the type.
Solenoid valves of this type are used widely in gas-burner supply systems, for regulating the input gas-flow and thus modulating the production of heat by the burner. A typical known solenoid valve comprises a hollow metal body with an inlet connector and an outlet connector with a valve seat, and a closure member movable along an axis perpendicular to the flow of the fluid. The closure member is connected or otherwise mechanically coupled to a ferromagnetic core which forms part of a magnetic circuit activated by a solenoid mounted on the body. The valve seat and the closure member are shaped in a manner as to define between them an aperture the size of which is variable continuously from zero, that is, from a position in which the flow of fluid is blocked, to a maximum value, that is, to a position in which the fluid has the maximum flow-rate, in dependence on an electrical control quantity, usually the current passing through the solenoid. Flow-rate regulating means may also be provided to ensure stable positioning of the closure member at all points of its travel and gradual movement of the closure member, without hysteresis. The hollow body is generally made of a ferrous alloy, by pressing or die-casting, and has structural and dimensional characteristics such as to ensure the necessary torsional and bending strength. It is generally quite heavy and bulky and constitutes a fairly expensive part of the solenoid valve. The adjustment means also constitute a critical part of the solenoid valve since they are often quite complex, requiring particular care and tight manufacturing tolerances, particularly when they comprise hydraulic position-control systems.
An object of the present invention is to provide a solenoid valve which does not have a conventional body such as that described above and which is therefore less bulky and expensive than known solenoid valves. This object is achieved, according to the invention, by a solenoid valve for delivering a fluid at a variable flow-rate, comprising a duct having an inlet opening and an outlet opening through which the fluid can pass substantially without changing direction, a valve seat within the duct, between the inlet opening and the outlet opening, a closure member movable between a closure position and a fully-open position, electromagnetic means for acting on the closure member in order to move it to any position, in dependence on an electrical control quantity, the electromagnetic means comprising a core of ferromagnetic material, fixed firmly to the closure member and movable substantially along the same axis as the fluid, and a solenoid for generating a force on the ferromagnetic core along the same axis.